rainwater tanks - health.nsw.gov.au · rainwater tank and allowed to stand for a minimum of two...
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rainwater can be disinfected by bringing to a rolling boil, and allowed to cool before drinking.
Is the water safe to drink?Generally yes. A properly maintained rainwater tank can
provide good quality drinking water. Providing the rainwater
is clear, has little taste or smell and is from a well maintained
water catchment system it is probably safe and unlikely to
cause any illness for most users.
Rainwater tanks are widely used as a source of drinking
water throughout rural Australia. Water used for household
purposes for drinking, food preparation or bathing should
meet water quality guidelines in order to protect you
and your family’s health. The water should be free of
harmful microorganisms or harmful levels of chemicals. By
far the greatest potential risk to your health comes from
contamination of water with harmful microorganisms such
as bacteria and parasites from bird or animal droppings.
Rainwater tanks can also be contaminated from roof or
plumbing materials.
The microbiological quality of rainwater collected in domestic
tanks will be poorer than that of many public water supplies.
Occasionally there are cases of illness from contaminated
rainwater. However, providing systems are well maintained
the risk of harmful organisms being present is low.
Premises that serve the public or employees and use
rainwater for drinking and/or cooking should comply with
NSW Health’s Private Water Supply Guidelines.
Rainwater tanks in urban areas
In urban areas the public water supply remains the most
reliable source of good quality drinking water for the
community. In these areas NSW Health supports the use
of rainwater tanks for non-drinking uses, such as toilet
flushing, washing clothes or in water heating systems, and
outdoors for uses such as garden watering, car washing,
filling swimming pools, spas and ornamental ponds, and
fire fighting. Use of rainwater conserves the public water
supply and helps to reduce stormwater impacts. In urban
areas NSW Health recommends that people use the public
water supply for drinking and cooking because it is filtered,
disinfected and generally fluoridated. The quality of public
water supplies is regularly monitored.
People who choose to use rainwater for drinking and
cooking should be aware of potential risks associated with
microbiological and chemical contamination. Rainwater
tanks in urban areas can be contaminated with airborne
contaminants from heavy traffic, smelters and heavy industry.
What if I have a weakened immune system?
People with special health needs such as those
who have a severely weakened immune system (the
Rainwater TanksWater is our most precious
natural resource and
something that most of us take
for granted. We are increasingly
becoming aware of the importance
of water to our survival and its
limited supply, especially in such
a dry continent as Australia.
Rainwater tanks can provide a
renewable supply of natural, soft,
clear and odourless water that can
be used for a range of purposes.
In some areas it may represent the
primary source of household water.
immunocompromised); including some people with HIV
and AIDS, transplant recipients, dialysis patients and cancer
patients; should talk to their doctor about potential risks
from drinking rainwater. These people, and the very young
or very old, may wish to take extra care by using only boiled,
bottled or micro-filtered water and avoiding foods and
beverages that may contain rainwater. Please contact your
doctor or local Public Health Unit if you require additional
information on this issue.
People should be aware of the dangers of scalding and be
careful when boiling water.
Fluoride
Rainwater does not contain fluoride. Where rainwater is the
major source of water for drinking and cooking, advice about
alternative sources of fluoride should be sought from your
local dentist, school or community dental service or from the
Australian Dental Association.
How can water quality be protected?
The provision of good quality water depends on correct
design and installation followed by sensible maintenance of
the rainwater tank and catchment area. The collection of
rainwater involves “low maintenance not no maintenance”.
It is good practice to flush rainwater taps used for drinking
or cooking for 2 to 3 minutes at the start of each day.
This is because water that has been standing for a long
time can dissolve metals such as copper and lead from the
pipework. This “first-flush” of water can be used for washing
up, watering plants or other non-drinking uses.
The tank
Tanks are available in a wide range of materials including
steel (galvanised and Aquaplate), concrete, fibreglass or
plastic. All of these materials can be suitable providing the
tanks have been manufactured specifically for the collection
of rainwater. It is also important to note that:
l Some PVC pipes may contain lead so if the water is
for drinking purposes, only high quality plastic pipe
and fittings should be used (‘drinking water’ not
‘stormwater’ grade).
l There have been some reports that water collected from
metal roofs can react with steel tanks to cause corrosion.
l Some types of new tanks may have to be washed or
flushed before use. The manufacturer should be able to
provide advice on whether this may be necessary.
When installed the tank should be covered to prevent light
from reaching the water, as it will encourage the growth
of algae. Every access point should be sealed unless in use.
The inlet and overflow of the tank should incorporate a mesh
cover and a strainer to keep out materials such as leaves
and to prevent the access of mosquitoes and other insects.
The top of the tank should have a tightly sealed access cover,
to stop animals and children entering but to allow access to
the tank for cleaning and inspection purposes. Any ground
level covers should also be sealed to prevent stormwater
entering in-ground tanks.
The catchment
In general, house and shed roofs are used as catchment
areas. Rainwater can be collected from most types of roofs,
including asbestos-cement roofs, providing they have not
been painted with lead-based paints or coated with
bitumen-based material.
Roofs coated with acrylic paints may contain dissolved
detergents and chemicals that can affect the colour or taste
of rainwater. The first few runoffs from these types of roofs
may need to be discarded. Rainwater collected from the first
few runoffs from new concrete tiled or metal roofs should
also be discarded.
As a precaution the use of pesticide-treated timbers and
lead flashing should be avoided in roof catchments. Also,
if possible, rainwater should not be collected from parts of
roofs incorporating flues from wood burners.
Overflows or discharge pipes from roof mounted appliances
such as evaporative air conditioners or hot water systems
should not be allowed to discharge onto the roof catchment
area.
First flush devices
First flush devices prevent the first portion of roof run-off
from entering the tank and will reduce the amounts of dust,
bird droppings and leaves etc, that can accumulate on roofs,
from being washed into tanks. The use of these devices is
recommended.
Alternatively the tank inlet should be disconnected so that
the first run-off of rain after a dry spell is not collected.
If your house is oversprayed by aerial chemical spraying,
divert the collection pipe from your rainwater tank to prevent
any pesticides from entering the tank. Clean the roof or wait
until after the next rainfall before reconnecting your drinking
water tank to your roof.
Tank maintenance
Proper maintenance of the tank, catchment system, roof,
gutters and inlet is essential to ensure a safe supply of water
and is best carried out before seasons when heavy rain is
expected.
Roof catchments and gutters should be inspected and
cleared of leaves and other debris every three or four months.
Overhanging branches should also be removed where possible.
If overhead wires are too close for safety, contact your local
power authority for advice.
All screens should be cleaned regularly. Tanks should not be
allowed to become breeding sites for mosquitoes. If mosquitoes
are detected in a tank the entry point should be located and
closed. For most types of tanks mosquito breeding can be
stopped by adding a teaspoon of domestic kerosene, which will
eventually evaporate. Power kerosene should not be used as it
will taint the water.
Desludging
Tanks should be examined for accumulation of sludge at
least every 2-3 years. If sludge is present in the tank it should
be removed by siphon or by complete emptying of the tank
(desludging).
Do-it-yourself tank cleaning presents a number of risks including
working in confined spaces. It is important to be aware of
occupational health and safety guidelines.
Tanks with a ‘cone scour’ base are easy to clean by simply
opening the cleaning outlet to allow the water to gush out with
the sludge then rinse with a hose. Small, flat-bottomed tanks
can be drained, rinsed with a hose and tilted to drain. One
method of cleaning big flat-bottomed tanks is to get inside with
a bucket, shovel and broom and dig out the sludge. A second
person should be present to ensure the safety of the person
inside the tank.
Clean a big tank early in the morning or when the area is
shaded to avoid heat exhaustion. For light inside the tank, use a
battery lantern not a flame or electric extension. If chemicals are
being used for repairs inside, a respirator may be necessary.
Professional tank cleaners are available in some areas.
A concrete tank could crack if it dries out. Check with the
tank supplier to find out if the type you have can safely remain
empty for a few weeks. It might be necessary to put water in
the tank to stop it from cracking.
Plastic tanks will need some water or should be tied down to
stop them from blowing over in strong winds when they are
emptied.
Disinfection
Rainwater can be disinfected by bringing to a rolling boil,
and allowed to cool before drinking.
Regular disinfection should not be necessary (unless required
on medical advice). However, if you suspect that water in
the tank is contaminated, it can be chlorinated by adding
powdered swimming pool chlorine (calcium hypochlorite,
65 per cent available chlorine) or liquid chlorine (sodium
hypochlorite, 12.5 per cent available chlorine). You should
not use stabilised chlorine (chlorine cyanurates).
It takes about 5 milligrams of chlorine per litre to disinfect
your tank. This is equivalent to 7 grams of calcium
hypochlorite or 40 millilitres of sodium hypochlorite per
1000 litres of water. A level dessert spoon may be used as
an approximate measure for 7 grams of powdered calcium
hypochlorite. A lot of the chlorine may be used up during
disinfection. There should be at least 0.5 milligrams per
litre free chlorine, 30 minutes after the chlorine is added
– you can use a pool chlorine test kit to measure how much
chlorine is in the water. Note that milligrams per litre is the
same as parts per million.
You should be able to smell the chlorine faintly an hour or
so after treating the water. If you can’t, you may need to
add a similar amount of chlorine again. Ideally the tank
shouldn’t be used for at least 24 hours to allow the chlorine
taste and smell to dissipate and for harmful microorganisms
to be destroyed.
To maintain a safe water supply after the initial dosage,
1 gram of calcium hypochlorite or 4 millilitres of sodium
hypochlorite per 1000 litres should be added to the
rainwater tank and allowed to stand for a minimum of
two hours. The water will be safe to drink provided the
chlorine smell is not too strong.
If the tank is your only source of water,
it can still be desludged regularly by
siphoning the sludge off. If the sediment
has been stirred up, the water can be
treated chemically with chlorine and/or
boiled before consumption. The best
arrangement is to have two tanks and
clean them out alternately.
Other forms of water treatment may also be used, such
as disinfection with ultraviolet light (UV) or filtration. Not
all filters remove or inactivate harmful microorganisms. If
a filter is used for health reasons, then it should meet an
appropriate standard (such as AS/NZS 4348 or ANSI/NSF
53). Units that incorporate boiling, distillation or reverse
osmosis processes are also satisfactory. An additional
disinfection unit may be necessary to inactivate bacteria.
It is important to follow the manufacturer’s instructions.
Filters should be correctly installed; maintained and replaced
regularly otherwise they will become ineffective and can
allow bacteria to grow that are then released into the filtered
water. Please contact your local Public Health Unit for further
advice on disinfection and filtration.
Water heating systems that operate between 60 and 70˚C
will kill harmful bacteria. The temperature should be 50˚C or
less at outlets used for personal hygiene. The temperature
should be 43.5˚C or less at outlets used for personal hygiene
in childcare centres, schools, nursing homes, or similar
facilities for sick, aged or disabled persons. Rainwater may
cause corrosion in water heating systems. Suppliers can
provide advice on modifying water heating systems to suit
rainwater. It is not recommended that water from the hot
water tap be used for drinking or cooking.
Choosing a rainwater tank
The size of the tank required to meet household needs will
depend on a number of factors including:
l �Rainfall�– the average annual rainfall, the pattern of
distribution throughout the year and the variation from
year to year
l Roof�Area�– which places an upper limit on the amount
of water that can be collected
l Acceptable�Level�of�Security�– the risk or possibility
of the tank running dry. A higher level of security will be
required where tanks are the sole source of supply
l Demand�– which varies enormously from household to
household and season to season depending on: number
of people in the household; their water use habits; what
the rainwater is used for and the number and type of
water saving appliances.
Where a tank is to provide an alternative or secondary supply
(eg to the public water supply), the size of the
tank is not such a critical issue and often will depend
on considering user requirements (garden watering,
car washing etc) balanced against cost.
What if I need more water from another source?
Rainwater may be supplemented by water from other
sources such as rivers, creeks and dams (surface water) or
bores (groundwater). However, water from these sources
may require additional treatment, such as filtration and
disinfection, to maintain water quality.
If you top up your tank from a water carter you should
ensure that you are being supplied with clean (potable)
drinking water from a clean tank. Waters Carters should
comply with the NSW Health Guidelines for Water Carters
and be registered with the local Council and NSW Food
Authority.
Where can I get more information?
l Your local Public Health Unit can provide
information on water quality and health (under
“Health Department of NSW” in the Telstra White
Pages or at http://www.health.nsw.gov.au/
public-health/phus/phus.html
l If you have any specific health concerns you
should discuss these with your family doctor.
l More detail about managing and using rainwater
tanks can be found in the book ‘Guidance on
the Use of Rainwater Tanks’, published by the
Australian Government for enHealth in 2004
(ISBN 0 642 82443 6). Printed copied can be
ordered from National Mail and Marketing on
(02) 6269 1000. Copies can also be printed from
the NSW Health website: http://www.health.nsw.
gov.au/public-health/ehb/water/rainwater.html
l The NSW Health Guidelines for Water Carters
are available at: http://www.health.nsw.gov.au/
public-health/ehb/water/drinkwater.html
l Many analytical laboratories can advise on
chemical, microbiological and algal testing of
water. If you wish to have some water tested
your local Public Health Unit can help you find an
accredited laboratory or look in the Yellow Pages
under the heading ‘Analysts’.
l Your local council can provide information on
any building or planning regulations for rainwater
tanks in your area.
It is important to mix the chlorine in a plastic bucket IN THE OPEN AIR before adding it to the tank. Mix it thoroughly with the tank water. Do not pour water into chlorine, always add chlorine to water.
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